Antennas & Feedlines Flashcards
7 cards from real Ham Radio Technician Test practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Antennas & Feedlines flashcards as text
What is the main advantage of a beam antenna (such as a Yagi) over a dipole for VHF weak-signal work?
Answer: Higher gain in a specific direction improves both transmit and receive performance
A beam antenna's directional gain increases effective radiated power on transmit and reduces noise from unwanted directions on receive.
Which feedline type is immune to common-mode RF currents without additional chokes?
Answer: Open-wire ladder line
Open-wire ladder line is balanced and symmetrical, so it does not support common-mode currents the way coax can.
What is the purpose of antenna radials on a ground-mounted vertical?
Answer: They provide a low-loss RF ground return to complete the antenna circuit
Buried or on-surface radials create a low-resistance ground system that minimizes losses in the soil and completes the antenna circuit.
If you double the number of radials on a ground-mounted vertical from 8 to 16, what is the expected result?
Answer: Reduced ground losses and improved antenna efficiency
Doubling radials reduces ground resistance and ground losses, increasing the power actually radiated by the antenna.
What does 'dBd' mean when specifying antenna gain?
Answer: Gain relative to a half-wave dipole reference antenna
dBd means decibels of gain compared to a half-wave dipole; dBi compares to an isotropic radiator (dBd = dBi − 2.15).
What is a common cause of RF feedback (RF in the shack) in a station with a coax-fed dipole?
Answer: Common-mode current flowing on the outside of the coax shield back into the shack
When coax is connected directly to an unbalanced dipole without a balun, RF can flow back on the shield outer surface into the operating position.
What is the typical characteristic impedance of open-wire (ladder line) feedline?
Answer: 300 to 600 ohms
Open-wire ladder line has a characteristic impedance of roughly 300–600 ohms depending on conductor spacing and wire diameter.